1. Field of the Invention
The present invention relates to animal behavior modification systems, and, more particularly, animal behavior modification systems which apply an electrical shock to an animal.
2. Description of the Related Art
Animals such as dogs may be fitted with a collar which carries a receiver unit and a pair of electrodes for applying electrical stimulation to the skin of the dog in order to control its behavior. For example, a conventional pet containment system includes a stationary transmitter which is connected to an endless wire placed around the confinement area under the surface of the ground. Over the endless wire, the stationary transmitter transmits a radio frequency (RF) signal which is received by the receiver unit if the dog approaches too close to the wire. In response to receiving the signal, a voltage is applied across the electrodes, which causes an electrical current to flow through the dog""s skin between the two electrodes. Alternatively, the trainer may carry a portable transmitter which selectively transmits an RF signal to the receiver unit for electrical stimulation when the animal exhibits undesirable behavior. As another option, a stationary transmitter may transmit an RF signal which is received by the receiver so long as the dog is in the confinement area. If the dog strays from the confinement area, the RF signal is no longer received and electrical stimulation is applied to the dog through the electrodes.
It is known to provide a voltage across the electrodes by using a high voltage, high output impedance flyback transformer with open circuit voltages ranging between approximately 3000V and 10,000V at the maximum levels. The transformer is small enough to fit within the confined housing on a collar placed around an animal""s neck. In order to generate the high voltage levels in a small package, the transformer has numerous turns of fine wire on the secondary coil and has an output impedance of greater than 1500 ohms.
A problem is that the electrodes can be at least partially shorted out or shunted by water between the electrodes. The water may be carried on the skin and/or fur of the dog, or the water may be completely surrounding the electrodes when the dog is submerged in water. This problem particularly occurs when the dog has been in the rain, or when the dog goes into a lake, such as while hunting. The water between the electrodes presents less electrical resistance (approximately 200-500 ohms) than does the dog""s skin. Thus, most of the current flows through the water, and the low level of remaining current which flows through the dog""s skin may not be enough to get the dog""s attention.
A related problem is that since the transformer""s output impedance of over 1500 ohms is so much greater than the resistance of the water (200-500 ohms), there is both a large voltage drop across the secondary coil and an impedance mismatch between the transformer and the load.
The large voltage drop across the secondary coil reduces the voltage that can be applied to the electrodes. The impedance mismatch limits the amount of power that can be transmitted from the transformer to the load. In dry loading conditions, in which the electrodes are pressed against the animal""s skin, the electroshock voltage levels drop to the hundreds of volts range, which is adequate to effect the desired electroshock stimulus. However, in water or in wet conditions, the electroshock voltage levels drop to several tens of volts, which may be completely undetectable by the animal.
It is also known to surround the sides of the electrodes with an electrically insulating material which blocks the flow of current through the adjacent water. Only the tips of the electrodes which contact the skin of the animal are left exposed. A problem is that the uninsulated electrode tips must be firmly pressed against and into the animal""s skin so that the skin effectively insulates the electrode tips from the surrounding wet fur. However, pressing the electrode tips tightly against the animal""s skin can lead to lesions and infections at the electrode contact site. For this and other reasons, many dog owners are reluctant to tighten the collar around the dog""s neck to the required degree.
Yet another problem is that internal arcing or corona discharges may occur within the receiver unit due to the transformer""s high output voltage (up to 10,000V) when the system is unloaded. The close spacing between the electrical components or traces within the receiver unit, as required by the dimensional limitations of the receiver unit, increases the likelihood of such electrical arcing.
What is needed in the art is a dog training collar which provides an effective electroshock stimulus to either a dry or wet animal without insulating the sides of the electrodes or burying the electrodes in the animal""s skin. Further, internal arcing due to the high voltages within the receiver unit must be avoided.
The present invention provides a dog training collar including a low impedance transformer which ensures that an adequate current is sourced through the animal""s skin, even in wet conditions. The open circuit output voltage of the transformer is limited.
The invention comprises, in one form thereof, a remote receiver unit for use in an animal behavior modification system that applies an electrical shock to an animal. The remote receiver unit has an electrical shock device including two electrodes configured for contacting the animal, a source of alternating current voltage, and an electrical transformer with a primary coil and a secondary coil. The primary coil is electrically connected to the source of alternating current voltage. The secondary coil is electrically connected to at least one of the two electrodes. The transformer has an output impedance of less than 900 ohms. A receiver circuit is electrically connected to the shock device. The receiver circuit is configured for activating the shock device in response to a received signal.
An advantage of the present invention is that an effective electroshock stimulus can be applied to an animal in a wet environment without insulating the electrodes and without the need for tightening the collar to such a degree that the electrodes are effectively buried in the animal""s skin.
Another advantage is that the open circuit output voltage of the transformer is limited to thereby avoid internal arcing within the receiver unit.